Thermoelectric conversion elements include a thermoelectric generating element, which generates power by use of heat, and a Peltier element, which transfers heat by use of electricity. Basic structures of the thermoelectric generating element and the Peltier element are the same.
A thermoelectric conversion element includes: a pair of heat transfer plates made of an insulator such as alumina with good thermal conductivity; p-type semiconductor blocks and n-type semiconductor blocks arranged between those heat transfer plates; and electrodes serially connecting the p-type semiconductor blocks and the n-type semiconductor blocks. Since it may not be possible to achieve a sufficient performance as the thermoelectric conversion element by using only one p-type semiconductor block and one n-type semiconductor block, the thermoelectric conversion element usually employs over ten to several hundreds of p-type semiconductor blocks and n-type semiconductor blocks. Specifically, a thermoelectric conversion module is usually formed by alternately arranging and connecting over ten to several hundreds of the p-type semiconductor blocks and the n-type semiconductor blocks in series between the pair of heat transfer plates. The thermoelectric conversion module includes a pair of extraction electrodes connected to both ends of an aggregate of the p-type semiconductor blocks and the n-type semiconductor blocks connected in series.
When a current is applied to the p-type semiconductor blocks and the n-type semiconductor blocks by connecting the pair of extraction electrodes to a power source, heat is transferred from one of the heat transfer plates to the other heat transfer plate by the Peltier effect. Meanwhile, when a temperature difference is applied between the two heat transfer plates, a potential difference is generated between the p-type semiconductor blocks and the n-type semiconductor blocks by the Seebeck effect, so that a current may be taken out of the extraction electrodes.    Patent Document 1: Japanese Laid-open Patent Publication No. 08-32125    Patent Document 2: Japanese Laid-open Patent Publication No. 2008-91442    Patent Document 3: Japanese Laid-open Patent Publication No. 11-32492
Incidentally, the thermoelectric conversion module is formed by combining the plurality of members having mutually different thermal expansion coefficients, namely, the heat transfer plates made of the insulator, semiconductor blocks made of semiconductor, the electrodes made of metal, and so forth. Moreover, the semiconductor blocks are usually connected to the electrodes by use of solder, but solder also has its own thermal expansion coefficient. For this reason, when a large temperature difference is repeatedly applied between the pair of heat transfer plates, a large strain (thermal strain) may repeatedly occur at junctions of the members and may lead to a disconnection.
As described previously, the plurality of p-type semiconductor blocks and the plurality of n-type semiconductor blocks are connected in series in the thermoelectric conversion module. Therefore, the thermoelectric conversion module may not function even with one disconnection.
Here, concerning a thermoelectric conversion system using a plurality of thermoelectric conversion modules, there is proposed a technique to provide a bypass circuit configured to detect conditions of the respective thermoelectric conversion modules and to automatically bypass a thermoelectric conversion module in which a failure has occurred. By using this technique, it is conceivable to restore the thermoelectric conversion module by bypassing a disconnected portion when a disconnection occurs in the thermoelectric conversion module. However, as described previously, the thermoelectric conversion module includes over ten to several hundreds of the p-type semiconductor blocks and the n-type semiconductor blocks. Accordingly, it is not practicable to prepare the bypass circuit for each of the semiconductor blocks because a huge number of the bypass circuits are necessary.